Modify Hop Up Chamber 1-Piece Metal for M4/M16 Series AEGs

The quality of this item is very good. Provides good seal with bucking. Adjustment gear has an o-ring behind it to keep the hop-up from backing down, if anything almost too hard to adjust (only reason I didn't give it 5 stars). Comes with two different hop up arms. No lateral movement of arm, fits snug in the metal body. Lastly, I give airsoftmaster.com VERY high praise. Free shipping on item, and they STILL sent it priority mail, instead of regular first class. Packaged well with lots of packing peanuts.